Radio receiving apparatus



Feb. 19, 1935. A. TAYLOR 1,992,019

RADIO REC EI VING APPARATUS Filed Aug. 5, 1951 2 Sheets-Sheet 1 l l iCUAHENTIN DETECTDR AND CIRCU T Inventor": Lauren 5 ATa lor';

y M SJWMM His Attor nel Feb. 19, 1935 1.. A. TAYLOR 1,992,019

RADIO RECEIVING APPARATUS Filed Aug. 5, 1931 2 Sheets-Sheet 2 Z'ivEInventor- Laurens ATaglor;

His Antorneg.

Patented Feb. 19, 1935 e Laurens A. Taylor, Schenectady, Pl. Y.,asslgnor to General Electric Company, a. corporation of New YorkApplication August 3, 1931, Serial No. 554,607

8 Clallnl. (Cl. 250-11) My invention relates to radio receiving appa- Afurther object of my invention is to provide ratus and more particularlyto that class of apconvenient and economical means whereby the paratuswhich is used for determining the direcsensitivity to direction ismaintained constant. tion of propagation of the received oscillations.The novel features which Ibelieve to be char- My invention has for oneof its objects to proacteristic of my invention are set forth with par-5 vide a directional receiving apparatus in which ticularity in theappended claims. My invention the sensitivity to direction is maintainedsubitself, however, both as to its organization and stantially constantat diiferent distances from, method of operation, together with furtherohthe source of the received oscillations. Thus, for jects andadvantages thereof, may best be underexample, it is well known that asdirectional restood with reference to the following description 10,ceiving equipment, as now employed, and which taken inconnectionwiththe accompanyi wmay include a directive antenna, such as a loop, ings inwhich Figs. 1 and 5 represent different is brought near to the source ofreceived oscillaembodiments of my invention; Fig. 2 represents tions,the sensitivity of the indicating instrument a modification of the"arrangement shown in 35 to the position of the loop increases. That is,as Fig. 1; and Figs. 3 and 4 represent certain charthe equipment isbrought near to the source of acteristics relative to my invention.received oscillations the index of the indicating Referring to Fig. 1 ofthe drawings, I have ininstrument deflects through increasing angles indicated therein a loop anten a. 1 and a vertical response to angularmovement of the antenna. a a e e a e a? being Shown in a Accordingly, ifthe index is to be maintained in nv n i nal w y to indicate y p f an nn20 a position corresponding to a predetermined dihaving respectivelydirective and non-directive rection a closer adjustment of the positionof the properties with respect to the direction of propaantenna isnecessary at positions near the source gation of the received wave. Thedirective anof received waves than at points distant theretenna 1 isconnected to supply oscillations to the from. When used on aircraft thischaracteristic inpu a amplifier 3, the Output O Which is 35 of theequipment greatly increases the difliculty coupled in the circuit of thenon-directive antenencountered in following a course leading toward na2. Thus oscillations from antenna 1 are amthe source of oscillations. Ifthe loop be one plified by the amplifier 3 and combined with which ismounted for movementonly in accordthose received from the antenna 2. Thecomance with the movement of the craft, the operbined oscillations aresupplied to the input cir- 30 ator in attempting to follow a courseleading cult of an amplifier 4 whereby they are amplified toward thesource of oscillations by the indicaby the device 4 and supplied to theinput circuit tions of the instrument receives the impression of adetector 5. Coupled to the output circuit of upon any deviation from thecourse that the the detector 5 by means of an audio frequency angle ofthe deviation with respect to the course transformer 6 is an audioamplifier '7, the output 35 is greater than is actually the case withthe reof which is supplied through a transformer 8 to suit that he isled to over steer and continuously a pair of headphones 9 and throughelectron disto' zigzag back and forth across the course in an chargedevices 10 and 11 to direction indicating effort to keep the needle inthe on course podevice 12.

sition. When at a distance from the source of Except in respects whichwill later be pointed 40 oscillations, however, the sensitivity of theinout, the circuits of discharge devices 3, 4, 5, and dicating device tothe position of the loop is '7 are of well known-form and will not bedereduced with. the result that the course is easier scribed in detail,it being sufiicient to point out to follow. These difficulties are alsoencountered that the anodes of these devices are all connected when theequipment is used to control the rudder through the primary windings ofthe respective 45 of the craft, as through an automatic steering outputtransformers to the positive side of a device. While automatic steeringequipment will source of potential 25 the negative terminal of not beshown in the present application, it is obwhich is connected to ground.The grids of deviously desirable that the response of such equipvices 3,4, and 7 are likewise connected through ment to deviation from thecourse be constant the secondary winding of the respective input 50throughout the length of the course; Thus, it transformers to ground andthence through biasis an object of my invention to provide a direcingmeans 17, 30, and 31 respectively to the cathtional system in which thesensitivity of response odes. The grid of detector 5 is provided with anis constant over large distances from the source individual source ofbias potential 30. The inof oscillations. put circuits of devices 4 and5 are, of course,

tunedintheusualwaywhereasthe theanodethroughtheprimary device! isaperiodic. The electron discharge amplifier 8 in addition toservingasanamplifier of theradiofrequency oscillations received-from thedirective antenna 1 alsooscillatesatacertainlow frequency, for example,1000 cycles. Thus it will be observed that the grid and anode circuit ofthis device are coupled together by windings 13 and 14 on an audiotransformer 15. The winding 13 isconnectedbetween thegrid andcathode andthe winding 14 is connected between the anode and cathode. this lattercircuit extending from g winding of radio frequency transformer 10,winding 14, condenser 16' to ground and thence from groundthroughaparallelcombinationofresistanceand capacitancel'ltotbecathodeofthedischarge device. The resistance and capacitance ofthis parallel combination 1'! are so proportioned as to provide asuitable bias on the grid of the amplifier 3 during operation thereof.This combination andthewindingiainseriestherewith,

cillations by means of a condenser 18 and similarly that portion of theanode circuit on the 'cathodesideoftheprimarywindingoftransformer iswith'respect to radio fre, quency oscillations by means of condenser 10.The frequency of the low frequency oscillationsisdeterminedbytheconstantsofthetransformer and condensers 18 and 19, andpreferably is in the neighborhood of 1000 cycles.

During operation of the device -3 to produce low frequency oscillationsits amplification with respect to the radio frequency oscillationsreceived from loop 1 varies in a sinusoidal manner. Thus. for. example,by proper adjustment of the circuits, at a point in the half cycle ofthe low frequency oscillations when a maximum of negative potential isimpressed upon the grid, the device may be inoperative to amplify0501118. tions received from the loop 1 whereas its ampliflcation ofthese oscillations increases to a maximum value during the successivehalf cycle of the low frequency oscillations. In this way the tube 3acts as a modulating device to modulate the oscillations received fromthe loop 1 with the oscillations generated within the tube itself and tosupply the modulated oscillations to the input circuit of the amplifier4 where they are combined with the oscillations received from thenondirective antenna 2.

The oscillations received from the antenna: 1 and 2 combine in the inputcircuit of the amplifler 4 either' in aiding or opposed relationdepending upon the position of the loop 1 and thereby cause theoscillations which are amplifled by the device 4 and detected by thedevice 5 to vary in a sinusoidal way, the sinusoidal variation having atime phase relation dependent upon the position of the loop 1. Thus inthe output circuit of the detector the low frequency oscillationsproduced by the device 2 are reproduced and have a time phase relationdependent upon the loop 1.

This operation of the device may best be understood by reference to Fig.4 in which I have plotted current in the detector anode circuit asordinates against time as abscissa. Thus, if we assume that oscillationsreceived from the antenna 2, which are of uniform intensity with respectto the direction of propagation of the received waves. cause a currentto flow in the detector anode circuit having a value correspondwithrupect to radio frequency os-' 11.1mm inputcircuit ing to the curve ofthe Pig. 4 then the oscillations received from the loop 1 throughamplifier 3, upon being combined in aiding or opposed relation "with theoscillations received from the antenna 2, cause the detector current tovary in a sinusoidal way as indicated by the curves 21 and22.Iftheloopiisinsucha position that the two oscillations combine in phasethen the oscillations impressed upon the input circuit of the amplifier4 and the detector 5 are maximum during that portion of the half cyclewhen the device 3 has maximum amplification, and accordingly, thecurrentin the detector '5 increased in accordance with thecurve 21. If,however, the loop 1 be in such aposition that the two waves combine inopposed relation then the oscillations impressed upon the circuits ofamplifier 4 and detector 5 are a minimum during those portions of thehalf cycle when the amplification of amplifier 3 is maximum. Thus thecurrent in the detector circuit will be reduced in a sinusoidal way asindicated by the curve 22. It'willbe observed that the curves 21 and 22are 180' displaced in phase and that this displacement in phase isproduced by movement of the antenna 1 between two positions. when theloop is in a position intermediate these two positions and correspondingtoa direction at right angles to the directions! the received waves nooscillations are received in the loop. Movement of the loop either tothe right or to the left from this intermediate position. however,causes a certain amount of energy to be received in the loop, theseoscillations having a certain time phase relation when the loop is movedin one direction from the intermediate position and a reversed timephase relation when the loop is moved in the opposite direction. Thus analternating current is produced in the output circuit of the detectorthe phase relation of which may be reversed by the movement of theantenna in one direction or the other with respect to the direction ofpropagation of the received wave. This alternating current wave isamplified by the device '7 and supplied through transformer 8 to thegrids of discharge devices 10 and 11 in opposite phase relation, thesegrids being connected to the opposite terminals of a secondary windingof the transformer 8.

The discharge devices 10 and 11 together with resistance 26 andinstrument 12 act as a phase indicating device to indicate the phaserelation between the low frequency oscillations reproduced by detector 5and those originally produced by the device 3. The low frequencyoscillations produced by device 3 are supplied from winding 24 ontransformer 15 to transformer 23, the secondary winding of which isconnected between the cathodes of devices 10 and 11 and the midpoint onthe secondary winding of transformer 8. Thus these oscillations areimpressed upon the grids in phase rather than in opposed phase relationas are those received from the transformer 8. Accordingly, theoscillations received from the transformer 23 and those received fromthe transformer 8 are applied to the grids of each of the dischargedevices 10 and 11 either in opposed or aiding relation dependent uponthe position of the antenna 1. The anodes of the two discharge devicesare connected together through the resistance 26 and are energized bymeans of a source of potential connected between ground and the midpointof this resistance. The course indicating instrument is connectedbetween opposite points on this resistance.

As thus arranged, it we assume that the antenna 1 is in a certainposition, such that the two oscillations supplied to the dischargedevice 11 are in phase, then a decrease in current in the ahode circuitof the discharge device 11 occurs; and simultaneously an increase in theanode current of the device 10 takes place since the two oscillationssupplied to the grid of that device are in opposed phase relation.Accordingly, a reduction in current in the lower part of resistance 28and an increase in current in the upper part of resistance 26 takesplace with the result that current fiows through the indicating device12 in a direction to cause the index thereof to deflect, for example,toward the right. If we now move the loop 1 to a position such that thetwo oscillations impressed on the devices 10 and 11 combine in aidingrelation on the grid of device 10 and in opposed relation on the grid ofdevice 11, then an increase of current takes place in the lower portionof resistance 26 and a diminution of current occurs in the upper portionthereof. The current in the indicating device 12 then reverses causingthe index to deflect to the left.

It will thus be observed that if the equipment be arranged upon anaircraft, for example, and the loop 1 arranged for movement with thecraft then a course in the direction of propagation of the receivedwaves may be followed by so guiding the craft as to maintain the indexof the indicating device 12 in a central position. If the craft turns tothe right or to the left from the course the needle of device 12deflects in the corresponding direction thereby informing the pilot thathe is oil course.

It is desirable, however, that the sensitivity of the indicating device12 to the position of the loop 1 and hence to the movement of the craftbe substantially constant as the craft approaches the source of thereceived oscillations. If the sensitivity of the indicating device 12increases as the craft approaches the source, then the diilicultiespreviously pointed out in following the course are encountered. Thiseffect may better be understood by reference to Fig. 3 in which thedifferent figure 8 patterns 2'7, 28, and 29 represent the patterns of anordinary loop when rotated about a vertical axis corresponding to thepoint common to all of the different patterns. Thus, for example, if theloop is at a great distance from the source of oscillations and occupiesthe position in which the index of the indicating instrumentis at thecentral point of its scale and is then rotated through 180, thedeflection of the index will vary in accordance with the right hand lobe2'7, the index returning to the center of the scale when the loop isreturned to its initial plane. If the rotation now be continued througha successive 180 thereby returning the loop to its initial position thenthe index deflects in the opposite direction in accordance with the lefthand lobe 27. The same operation occurs when the loop is brought nearerto the source of oscillations but the deflection of the instrument isgreater as is indicated by the lobes 28 and 29 of larger radii.

It will be observed that if points of equal distance from the origin andcorresponding to equal deflections from the origin be marked off on thedifferent lobes as, for example, points A and B, and that lines 0A andOB be drawn through the origin and these points, these lines makedifferent angles :11 and a: respectively with a line 00 correspondingtothe true course when the index of the instrument occupies the "oncourse" position. Accordingly, if the craft is at a distance from thesource such that a deflection of the instrument corresponding to thevalue 0A indicates a deviation fromthe course by an angle on and thenproceeds to a position such that an equal deflection of the instrumentis produced in response to deviation from the course by a much smallerangle as, the pilot is likely to be misled by the latter indication withthe result that he repeatedly oversteers and finds'difilculty infollowing the course. The deflection of the instrument therefore is nota satisfactory indication of the angle between the loop and the course.

To overcome this effect means are provided in accordance with myinvention for controlling the amplification of the amplifier 4 inaccordance with the intensity of oscillations received by the verticalantenna 2. This means comprises a resistance 30 connected in the anodecircuit of the detector between ground and the cathode. The potential onthis resistance is supplied between the cathode and grid of thedischarge device 4 through conductors 32 and 33. Thus, as the craftapproaches the source of oscillations, the current in the anode circuitof the detector increases thereby causing the grid of amplifier 4 tobecome more negative with respect to the cathode, this effect in turnreducing the amplification of the discharge device 4. In this way theamplification of the device 4 is so controlled that the intensity of thelow frequency oscillation which is reproduceddn the anode circuit of thedevice 5 is maintained substantially constant irrespective of theintensity of the oscillations received from antenna 2.

It will be observed that a condenser 34 is connected in parallel withthe resistance 30 and that an additional condenser 16' is connected inparallel with the source of anode potential 25. The capacitance of thesecondensers is so chosen that the time constant of the automaticsensitvity control means is such that it does not respond to variationsin intensity of oscillations supplied thereto which occur due tovariation in the amplification of amplifier 3 whereby the amplificationof device 4 is controlled only in accordance with the gradual variationswhich take place as during movement of the equipment toward or away fromthe source of oscillations. Thus the amplification is controlledsubstantially in accordance with the intensity of oscillations receivedfrom the antenna 2 and independently of the intensity of oscillationreceived through the amplifier 3.

It will thus be observed that with the equipment as thus describedadjusted to operate, for example, in accordance with the curve 2'1 ofFig. 3, its operation will be in accordance with this curve 2'?throughout the entire course of the craft toward, or away from, thesource of oscillations and accordingly the sensitvity of the indicatingdevice to the position of the loop remains constant. It will be observedfurther that this effect is one which is not due entirely to thesensitivity control means 30, 32, 33 but instead results from thecombination with the directive and non-directive antenna: 1 and 2 asindicated.

In Fig. 2 I have shown a modification of the arrangement shown in Fig. 1in which the locally produced oscillations are supplied from anindependent source 35 through the transformer to the grid of amplifier 3thereby sinusoidally to vary the amplification of that device. Thus inaccordance with this modification of the invention the coupling betweenthe anode circuit and grid circuit which is produced by the winding 14of Fig. 1 is eliminated. Oscillations from an independent source in thisfigure are also supplied to the transformer 23 as shown in Fig. 1.

In Fig.5 I have shown a further embodiment of my invention which differsfrom that shown in Fig. 1 in respects which will be presently explained.In the arrangement of this figure the loop 1, in addition to serving asa directive anthereof from the secondary winding 37 on a transformer 36the primary winding of which is connected to the local source ofoscillation 35.

The course indicating instrument in this figure comprises a simpletwo-winding indicating,

device 41 of the wattmeter type, one of the windings of this instrumentbeing supplied with low frequency oscillations which are reproduced bythe detector 5 and the other winding 42 being supplied with oscillationsdirectly from the source 35. Thus the index of this instrument moveseither to the right or to the left dependent upon whether the currentsin the two windings are in phase or in opposed phase relation.

In the arrangement of this figure the detector 5 serves only todemodulate the high frequency wave, the automatic sensitivity controlbeing effected by means of an additional detector 5' the control grid ofwhich is connected in parallel with the detector 5. The automaticsensitivity control resistance 30 is connected in series with the anodecircuit of this device the potential on a portion of this resistancebeing supplied between the grid and cathode of the amplifier 4 throughconductors 32 and 33. Connected between the conductors 32 and 33 are aplurality of condensers 43, 44, and 45 between adjacent con- .densers ofwhich are connected resistances 46 and 47. This condenser resistancecombination constitutes a network the time constant of which is suchthat the potential supplied to the grid of the discharge device variesonly in accordance with the gradual variations in potential onresistance 30 which occur as the result of variations in intensity ofoscillations in the non-directive antenna circuit and is substantiallyunaffected by intensity variations produced by the device 3.

It may occur, however, that the bias potential upon the grid of device 3will vary to a certain extent at the low frequency rate notwithstandingthe use of the network 4347. To overcome this effect means are providedwhereby current in the anode circuit of detector 5' is controlledsynchroncusly with the modulation which is effected by the. amplifier 3.1 This control is effected by means of a screen grid within thedischarge device 5' and which similarly with device 3 is supplied withpotential from the source 35 through the transformer 36. Thus a secondsecondary winding 37 on transformer 36 is connected between the screengrid and cathode of the device 5; The intensity of the oscillationssupplied to the screen grids of the amplifier 3 and detector 5' may becontrolled by potentiometers 38 and 39 connected respectively across thewindings 37 and 38'. By proper adjustment of the potentiometer 38 anyresiduum of variation in potential between conductors 32 and 33 at thefrequency of the source 35 may be eliminated thereby producing a steadybias potential upon 7 the grid of device 4 the intensity of which variesthat I do not wish tobe limited thereto since many modifications both inthe circuit arrangement and in the instruments employed may be made, andI contemplate by the appended claims to cover any such modifications asfall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a directive antenna circuit, a non-directive antennacircuit, a source of low frequency oscillations, means for modulatinghigh frequency oscillations received from said directive antenna circuitwith said low frequency oscillations and for combining said modulatedoscillations with oscillations received from said non-directive antennacircuit, an indicating device, means for reproducing said low frequencyoscillations from said high frequency oscillations and for supplyingsaid low frequency oscillations to said indicating device, means forsupplying low frequency oscillations directly from said source to saidindicating device and means for main taining the relative intensitybetween said oscillations supplied to said indicating devicesubstantially constant irrespective of variations in intensity ofoscillations received from said nondirective antenna circuit.

2. In combination, a directive antenna circuit, a non-directive antennacircuit, a source of low frequency oscillations, high frequencyoscillations received from said directive antenna circuit with said lowfrequency oscillations and for combining said modulated oscillationswith oscillations received from said non-directive antenna circuit,means to amplify said combined oscillations, means to reproduce said lowfrequency oscillations from said combined oscillations, indicating meansresponsive to the phase relation between said reproduced oscillationsand the low frequency oscillations of said source and means forautomatically controlling the amplification of said amplifying means inaccordance with the intensity of oscillations received from saidnon-directive antenna circuit and irrespective of the intensity ofoscillations received from said directive antenna circuit.

3. In combination, an antenna, means to modulate oscillations receivedfrom said antenna with local oscillations, means to amplify themodulated oscillations, and means controlled by said local oscillationsfor automatically governing the amplification of said amplifying means.

4. In combination, a directive antenna circuit, a non-directive antennacircuit, means to modulate oscillations received from said directiveantenna with local oscillations, means for combining said modulatedoscillations with oscillations received from said non-directive antennacircuit andamplifying the combined oscillations, means responsive to theintensity of the amplified oscillations and to said local oscillationsfor controlling the amplification of said amplifying means and means todemodulate said local oscillations, whereby said loc'al oscillations arerepromeans for modulating 'received from either of said antennacircuits.

5. In combination, an antenna, an amplifier for amplifying oscillationsreceived from said antenna, means for modulating said oscillations priorto amplification by said amplifier, means responsive to the intensity ofsaid oscillations for controlling the amplification of said amplifier,and means for controlling said last means synchronously with themodulation produced by saidmodulating means whereby said means isresponsive only to gradual variations in the intensity of saidoscillations and is unresponsive to said modulation.

6.- In combination, an amplifier, a directive antenna, a non-directiveantenna, means for supplying oscillations received from both of saidantennae to said amplifier for amplification thereby, a detectorconnected to the output of said amplifier, means responsive to directcurrent flowing in said detector to control the amplification of saidamplifier, a local source of oscillations, means for modulating theoscillations received from' said directive antenna prior to saidamplification in accordance with said oscillations from said localsource and for synchronously controlling said detector, whereby theamplification of said amplifier is varied only in accordance withgradual variations in the intensity of said received oscillations, andmeans responsive to the time-phase relation of the modulation of saidamplified oscillations to indicate the position of said non-directiveantenna with respect to the direction of propagation of received waveswhereby said means is substantially equally sensitive to the position ofsaid antenna at different distances from the source of the receivedoscillations.

7. In combination, an amplifier, means for supplying high frequencyoscillations modulated at a low frequency to said amplifier, means for'controlling the amplification of said amplifier in response to gradualvariations in intensity of said high frequency oscillations and meanssynchronouswith the low frequency modulation of said oscillations toneutralize the effect of said last means in reducing said low frequencymodulation.

8. In combination, an electron discharge amplifier having a grid, meansfor supplying high frequency oscillations modulated at low frequency tosaid amplifier, an electron discharge detector connected to receiveoscillations from said amplifier, said detector also having a grid,means responsive to direct current in said detector to supply biaspotential to the grid of said amplifier thereby to control theamplification thereof, and means for supplying low frequencyelectromotive force synchronous with the modulation of said highfrequency oscillations to the grid of said detector thereby toneutralize the efiect of said detector in reducing said low frequencymodulation.

LAURENS A. TAYLOR.

